Snow Cloak causes evasion to increase by 20% in a hailstorm. Even if a
Pokémon which is not of the Ice-type acquires this Ability, it will be
immune to the effects of hail.
Outside of battle
If a Pokémon with Snow Cloak is leading the party in an area with a
blizzard, then Snow Cloak decreases the wild Pokémon encounter rate by
Ice Body regains your HP while hail is active.
Hope I helped!